In Parasyte: The Grey, humanity is wreaked by parasites that fall from the sky, take over human hosts, and aim to control human civilization. The series is now streaming on Netflix.
Warning: This article contains heavy spoilers
Plot summary
Jeong Su-in, a supermarket employee, gets into an argument with a disrespectful customer, who seeks revenge on her.
He follows her and manages to stab her a few times. Su-in makes a run for it but passes out halfway. An organism near her takes control of her body. The attacker is then cut in half.
The case is reported to Detective Kim Chul-min, who shares a close bond with Su-in. When Su-in was a kid, she reported her abusive father to the cops, and it was Chul-min who saved Su-in.
To this day, Su-in looks up to Chul-min, and even he cares a lot about her. After the accident, Su-in realizes she has changed quite a bit but struggles to understand herself.
Meanwhile, at Namil Police Station, a Special Task Force from Seoul visits to brief the cops. The Special Task Force is the Grey Special Forces Unit, led by Choi Jun-kyung. They scan everyone before letting them enter the building.
Jun-kyung introduces the cops to the parasitic organisms that have been wreaking havoc recently, giving an example of the EDM festival, where a parasite, which has tentacles and eyes on its head, killed humans.
These parasites came in a kind of larval state a few months ago, appearing all over Korea and the world. These parasites take control of their host’s brain and body. They then follow their instincts to devour human life and survive.
Their heads can transform completely, controlling the rigidity and power of their cranial transformation and use it as a sharp blade to kill.
These parasites can be killed by destroying the body of their host. One can either bleed out the body all at once or aim for the heart.
These parasites are currently forming a cult of their own. However, since humans have become exposed to parasites, they have started conducting their research on these organisms, not giving them a chance to examine their existence.
Jun-kyung’s husband is in control of a parasite and she has captured him. These beings can’t reproduce, so they aim to survive. They can sense each other’s presence, and Jun-kyung is using her husband to track them and kill them.
While Namil Police Station is being informed about this, Su-in gets to know the parasite that has made a home inside her, who is later named Heidi by Kong-woo.
This parasite is unlike others out there; it has mutated because it took control of a dying Su-in. All of its energy went into healing Su-in, which is why it was not able to take full control of Su-in’s brain.
Now, the parasite can control Su-in for only 15 minutes a day or whenever Su-in is in danger to ensure its survival, as it shares Su-in’s body.
Assuming that the parasite inside Su-in is one of their kins, the parasites invite her to the church where they all gather.
Amidst all of this, Seol Kang-woo, a gang member, finds out that a parasite has taken control of one of his sisters, Seol Kyung-hee. Kang-woo finds the body of his other sister, Jin-hee, at one of the parasites’ hideouts.
Kang-woo and Su-in cross paths twice. The second time, he is saved by her. The two start working together.
In the meantime, while working with Team Grey, Chul-min starts finding evidence that leads to Su-in.
Even Su-in and Kang-woo opt to take Chul-min’s help. However, Jun-kyung’s team interferes and ruins things before the two parties can come to an understanding.
The parasites, on the other hand, have a human working for them in the form of Detective Kang Won-seok, who kills Jun-kyung’s husband, whose body possesses the parasite that humans are using against other parasites.
Jun-kyung arrests Su-in and uses her against the parasites now. Kang-woo has seen Won-seok kill Jun-kyung’s husband. He shares this with Chul-min and starts working with him.
The two are able to rescue Su-in, but Won-seok takes Chul-min to the leader of the parasites. The leader kills Chul-min, snatches Chul-min’s body, and sneaks into Team Grey.
With Chul-min gone, Kang-woo thinks it’s better they lie low now, but a heartbroken Su-in doesn’t seek this easy way out.
Su-in, time and again, attempts to tell their side of the story to Jun-kyung and convince her that she is not the enemy here, only to fail.
Over time, Jun-kyung starts investigating the claims Su-in has made and suspects that there is some truth in it.
In the meantime, the parasites, who are getting accustomed to human emotions, face betrayal from their kind, resulting in them getting divided.
Ending explained:
The parasites’ goal
Chul-min, who is under the control of a parasite, and Won-seok lure Jun-kyung’s team into a trap. However, to Su-in and Kang-woo’s surprise, they sacrifice some of their kind.
Kyung-hee, who is also under the control of a parasite, sees this as a betrayal. She quits the group.
Su-in and Kang-woo fail to understand this move until they see the poster for the Folk Music Festival that will be held for the opening of Choi Yong-jae Memorial Hall.
Jun-kyung’s seniors wanted the parasite problem to be solved before this big event. Namcheon’s mayor is attending the event.
There is a chance that the parasite in Chul-min’s body is secretly planning to take over a human leader’s body to slowly start taking over the entire human civilization.
Stopping Chun-mil
Kyung-hee joins hands with Su-in and Kong-woo after seeing how Chun-mil betrayed their kind.
At the festival, the mayor arrives. Su-in distracts Jun-kyung, while Kyung-hee faces Chun-mil. The parasite leaves Chun-mil’s body to capture the mayor’s.
Kyung-hee dies protecting the mayor and Kong-woo from the parasite. Eventually, Su-in comes to the rescue as Heidi.
Heidi and the parasite, who has now taken over Won-seok’s body, face each other until Jun-kyung arrives and holds Heidi at gunpoint.
Heidi shows trust in Jun-kyung, who attacks the parasite instead, while Heidi does the same. The two successfully defeat the parasite.
The fate of all the characters
Following this event, everyone gets back to their lives. Su-in starts working at the supermarket again.
Kong-woo, who now works for Team Grey, visits Su-in to hand her a message from Heidi. It seems like the parasite has left Su-in’s body to her.
However, it is hinted that Heidi continues to reside in Su-in. The last message from Heidi reads that Su-in is not alone, whether she likes it or not.
Kong-woo also lets her know that she has a place on Team Grey if she intends to join them.
Kyung-hee is visited by a journalist named Shinichi, who claims to be an expert in the field of parasites. He says he has some important intelligence to offer. Shinichi’s introduction and background music hint that he is someone shady.